Both my Milwaukee and M3 regulators decided to whistle on me too. Their pressure relief valves aren't glued in and over the years they came unscrewed. I put my thumb on top of them and screwed them back down with no tool. No more whistling. It was bizarre that this happened to both regulators the same week but those valves were rattling and about to fall out I really don't think it was a problem with too much gas in the tank or anything like that. I seriously doubt that is what is going on with your regulator, it is a much better built one and if the valve is glued down it isn't going to get loose.